As a microscope by which a sample can be enlarged and observed, there is a charged particle microscope using a charged particle beam such as electrons or ions. In particular, a scanning electron microscope (hereinafter, abbreviated as SEM) that images by scanning an electron beam on a sample has been used for a sample analysis such as an observation of a fine surface shape or a local composition analysis. The SEM is a microscope that analyzes a sample in such a manner that an electron beam accelerated by a voltage applied to an electron source is irradiated onto the sample, and the focused electron beam (primary electrons) is scanned on the sample by a deflector.
In particular, when a target to be analyzed is an insulator, the sample is charged by the irradiation of the electron beam, resulting in image disturbance such as drift or shading. Accordingly, in order to perform a stable sample observation that is high in reproducibility, an electrification control technique by the irradiation of an electron beam is essential.
Further, the SEM is expected to observe a sample having a laminated structure. The amount of charges of a sample is dependent on electrical characteristics such as the capacity and resistance of the sample, and further reflects a structure buried in the laminated structure or an interface of the laminated structure. Thus, the buried structure or the interface of the laminated structure can be observed by extracting the potential contrast due to the electrification of the sample.
As a related technique, Patent Literature 1 focuses on the fact that an image reflecting the buried structure appears in a specific time region in which a difference between secondary electron signals occurs, and describes a technique in which a sample is charged by intermittently irradiating an electron beam to select a secondary electron signal reflecting necessary sample information on the basis of a detection time. As an example of the detection time, an embodiment in which a detection time of 0.2 ms relative to a pulse irradiation electron having a pulse width of 0.5 ms is set and an embodiment in which a detection time of 0.05 ms in synchronization with a pulse having a pulse width of 0.05 ms is set are described.